Now the vehicle is working harder and harder to catch up to the set point, but it cannot. If you now change the depth to surface, the set point will move towards the surface. Depending on how far down you drove the set point, this could take quite a while before it is back above the bottom depth.

In this case it may be better to turn auto depth off and back on and then back on again, which will reset the set point to the current depth of the vehicle immediately.